came back from a meetup so I alighted at Lakeside MRT , so when I was about to tap out , the reader read "overstay" so I went to passenger service and the staff told me that i need to tap out , and i see that the last time i tap out was at Clementi , so is there a time limit ? anyone got this kind of thing before ?

This is because people misuse the system for buyer/seller meetup at MRT station. Usually the seller will pass the item from within gantry the buyer waiting outside. Seller gets free transport by taking a train back and exiting the origin station.